Added German translation.

● Added Russian translation.

● Added Ukrainian translation.

Added Turkish translation.

● Added Chinese translation.

● Added Czech translation.

● Added Polish translation.

● Enabled smaller step intervals for filter values so that you can tune settings more precisely.
● Improved display of gamma value.
● Facilitated extension translation via https://lusito.github.io/web-ext-translator/?gh=https://github.com/PyvesB/night-video-tuner
● Optimised images so that the extension menu loads faster.
● Removed update notification so that the extension requires less permissions.
● Various other improvements and cleaning up.

● Added gamma filter.

● Several under the hood enhancements.
● Added tests to improve maintainability.

● Fixed outline of selected elements in some browsers.

● Improved layout of the main menu.
● Improved some displayed texts.

● Fixed encoding warnings that would appear in some cases.